SHORT COMMUNICATION Detection of Cytotoxic Necrotizing Factor Types 1 and 2 among Fecal Escherichia coli Isolates from Brazilian Children with and without Diarrhea

The enteropathogenic role of cytotoxic necrotizing factor (CNF)-producing Escherichia coli was investigated by searching cnf genes among 2074 isolates from 200 children with and 200 without acute diarrhea in Brazil. Four-teen (7%) cases versus 10 (5%) control children carried at least one cnf positive isolate (P = 0.50) and most isolates expressed CNF type 1. DNA sequences of virulence factors of extraintestinal pathogenic E. coli (ExPEC) were detected in 78.6 % of CNF1-producing isolates. Besides not being associated with human acute diarrhea, the CNF1-producing isolates here identified may represent potential ExPEC transitorily composing the normal intes-tinal flora. Key words: Escherichia coli- cytotoxins- cytotoxic necrotizing factor- adhesins Cytotoxic necrotizing factor (CNF), a toxin firstly de-tected in extracts of Escherichia coli isolates from chil-dren with acute diarrhea in Italy, induces the progressive formation of multinucleated cells in certain cultured lines (CHO, Vero, HeLa, HEp-2), necrosis in the rabbit skin and in the mouse footpad, and death of mice inoculated by the intraperitoneal route. Two types of CNF have been identified (CNF1 and CNF2) and the cell activities of these toxins are due to their ability to constitutively modify the Rho proteins, a family of small GTPases that regulate the physiology of cell cytoskeleton (De Rycke et al. 1999). The single structural gene encoding prototype CNF1 (cnf1) is located on a chromosomal pathogenicity island, which has also the codifying genes for α-hemolysin (hly) and P-fimbriae or pyelonephritis-associated pilus (pap), whereas the cnf2 gene is located on a high-molecular weight plasmid (De Rycke et al. 1999). CNF1 is frequently produced by extraintestinal pathogenic E. coli (ExPEC) isolated from humans with urinary tract infection (D